The present invention generally relates to the manufacture of substrates, and in particular semiconductor substrates, for use in electronics, optoelectronics or optics.
Transfer techniques are used more and more frequently to manufacture such substrates, wherein more or less thick layers are transferred from one support to the other. In numerous applications in the field of microelectronics, therefore, a thin semi-conductive layer present on the surface of a first substrate (donor substrate) can be transferred to a second substrate (target substrate). Typically, this thin layer will be epitaxially grown, and prior to transfer will have undergone at least some of the technological stages utilized for manufacturing components. For example, a thin layer made of gallium nitride GaN can be arranged to include a fragile interface at the center of the first substrate to define a zone of weakness. Transfer is accomplished by first placing the exposed face of the thin layer, borne by the first substrate, in contact with a face of the second substrate. Adequate adhesion is ensured between the two contacting faces, and then detachment is carried out between the first substrate and the thin layer at the zone of weakness.
In general, different ways of producing a fragile bond are already known. A first technique consists of implanting ionic gaseous species, then submitting the implanted weakened zone to thermal and/or mechanical treatment or to another energy source, to a breaking point, as described for example, in U.S. Pat. No. 5,374,564. Another known technique consists of producing a layer of embedded oxide and attacking this layer by etching, as described, for example, in U.S. Pat. No. 6,027,958. Other known solutions consist of obtaining a fragile interface by creating a porous layer, as described, for example in document U.S. Pat. No. 6,100,166, and optionally implanting gaseous species into this layer to weaken it to the desired extent. An alternative to such processes that provide a zone of weakness, is a process consisting of eliminating the first substrate by a mechanical-chemical softening method, as described, for example, in published International Application No. WO 99/25019 A1, the major drawback being a significant loss of material.
It is also known to define the fragile plane by defining the interface between two different materials, and then submitting them to a specific treatment. Thus, in the case of a structure that includes a thin layer of gallium nitride GaN on a first substrate made of sapphire (Al2O3), the thin layer can be transferred by a technique known as laser lift-off. Laser lift-off consists of irradiating the GaN/sapphire interface using a laser to decompose and thus weaken the interface to the desired extent, and then cause detachment (in particular, see U.S. Pat. No. 6,071,795).
The adhesion of the free face of the thin layer and of the target substrate can be undertaken by a number of known processes. For example, an adhesive agent such as a duroplastic or photo-treatable glue could be used, as could anodic sealing, eutectic gluing, metallic fusion, and the like.
Detachment of the donor substrate and the thin layer is typically accomplished by applying mechanical traction forces and/or shearing forces and/or flexing forces. For example, a blade (see especially W. P. Maszara, G Goetz, A. Caviglia, J. B. McKiterrick, Journal of Applied Physics, vol. 64, p. 4943, 1988), or a fluid jet could be used, as described in International Patent Application No. WO 01/04933 A1.
There are disadvantages associated with each of the different known processes. First, it can be difficult to master or control the effective bond forces at the weakened interface which could make detachment difficult, if not impossible to accomplish. Consequently, the mechanical forces required to cause detachment can be substantial, which risks deterioration or breakage of the substrates. This risk is even higher in the case where such forces, or part of these forces, are applied by hand by using a tool.
Accordingly, there is a need for improvements in these type processes, and these improvements are now provided by the present invention.